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I can't believe the number of times I have been asked that question but it has just come up again in the context of recent complaints about the health and environmental hazards of eating meat. So here, once again, is my nutrition academic's take on the nutritional implications of vegetarian diets.
Full disclosure: I eat meat. Humans are omnivores and I am one nutritionist who fully subscribes to basic, if banal, principles of healthful diets: variety, balance, and moderation. As I explain in my book, What to Eat, if you eat a variety of foods within and among groups--meat, dairy, fruit, vegetables, and grains--you don't have to worry about nutritional details. As long as calories are adequate and the foods are relatively unprocessed, the different kinds of foods complement each other's nutrient contents and provide everything that is needed in reasonable amounts and proportions.
With that said, it is not necessary to eat meat. Meat is not an essential nutrient. I can think of plenty of advantages to eating no meat, eating less meat, or eating meat produced in ways that are far better for the health of animals, people, and the planet.
Except for the most restrictive diets, I wouldn't worry at all about vegetarian diets for adults or for kids.
Why anyone would question the benefits of eating vegetarian diets, or diets that are largely vegetarian is beyond me. People who eat vegetarian diets are usually healthier--sometimes a lot healthier--than people who eat meat.
But before getting into all this, there is the pesky problem of definition. What, exactly, is a vegetarian? As it happens, people who call themselves vegetarians eat many kinds of diets. The least restrictive vegetarians do not eat beef but occasionally eat pork or lamb. Next come the groups that eat no red meats, or restrict poultry, dairy, fish, or eggs. The most restrictive are vegans who eat no foods of animal origin at all.
Nutritional implications depend on the degree of restriction. The least restrictive diets, those that exclude meat but include fish, milk, or eggs, raise no nutritional issues whatsoever. People who eat such diets are likely to have a lower risk of heart disease and certain cancers than the average meat-eating American, and a risk of osteoporosis no higher.
Only the most restrictive vegetarian diets raise nutritional concerns. Vegans, who eat no foods of animal origin, need to do three things:
• Find an alternative source for vitamin B12 (supplements or fortified foods).
• Eat enough calories to maintain a good weight.
• Eat a variety of grains and beans to get enough protein.
Vitamin B12 is found only in foods of animal origin--meat, dairy, eggs, or fish. With this one exception, fruits, vegetables, and grains provide plenty of the other vitamins and minerals. Vegans who obtain enough calories from varied plant food sources should be taking care of those nutrients as well as protein.